Fluid angular rate sensor

ABSTRACT

An improved fluid readout means for devices that measure the angular rate of rotation of a body about an axis. A slotted cylinder is positioned in the drain of a vortex rate sensor, with its axis transverse to the drain axis. The slots are located in the upstream portion of the cylinder and are at a very small radius from the drain axis. As the helical angle of the flow through the drain changes due to change in rotation of the rate sensor the static pressure at the slots changes, and the pickoff produces a fluid output signal which is proportional to the angular rate of rotation of the sensor. Increased sensitivity may be achieved by introducing an airfoil section upstream of and in close proximity with the slotted cylinder. Alternatively, an airfoil section can be positioned to extend completely across the drain and serve to direct the helical flow to a splitter located downstream of the airfoil to produce a high flow output signal that is proportional to the angular rate of rotation of the sensor.

United States Patent Scudder et al.

[111 E Re. 28,622

[ Reissued Nov. 25, 1975 FLUID ANGULAR RATE SENSOR [75] Inventors:Kenneth R. Scudder, Chevy Chase;

John F. Burke, Beltsville, both of Md; John L. Dunn, Fairfax, Va.

[73] Assignee: The United States of America as represented by theSecretary of the Army, Washington, DC.

[22] Filed: July 17, 1969 [21] Appl. No.: 863,391

Related US. Patent Documents Reissue of:

[64] Patent No.: 3,365,955

Issued: Jan. 30, 1968 Appl. No.: 524,358 Filed: Feb. 1, 1966 [52] U.S.Cl. 73/505 [51] Int. Cl. G01p 3/26 [58] Field of Search 73/515, 505,194; 137/815 [56] References Cited UNITED STATES PATENTS 3,203,2378/1965 Ogren 73/194 3,272,213 9/1966 Jones 73/194 3,276,259 10/1966Bowles et a1 73/194 3,319,471 5/1965 Hermann 73/505 3,319,471 5/1967Hermann... 73/194 XR 3,320,815 5/1967 Bowles 73/194 [57] ABSTRACT Animproved fluid readout means for devices that measure the angular rateof rotation of a body about an axis. A slotted cylinder is positioned inthe drain of a vortex rate sensor, with its axis transverse to the drainaxis. The slots are located in the upstream portion of the cylinder andare at a very small radius from the drain axis. As the helical angle ofthe flow through the drain changes due to change in rotation of the ratesensor the static pressure at the slots changes, and the pickoffproduces a fluid output signal which is proportional to the angular rateof rotation of the sensor. Increased sensitivity may be achieved byintroducing an airfoil section upstream of and in close proximity withthe slotted cylinder. Alternatively, an airfoil section can bepositioned to extend completely across the drain and serve to direct thehelical flow to a splitter located downstream of the airfoil to producea high flow output signal that is proportional to the angular rate ofrotation of the sensor.

14 Claims, 11 Drawing Figures Reissued Nov. 25, 1975 Sheet 2 of2 Re.28,622

M m WM mm @m TLK wmvraes, /(5'A/A/E7H E scupaEz JOHN E BU/ZKE JOHN L.DUN/V 1 FLUID ANGULAR RATE SENSOR Matter enclosed in heavy brackets I: 1appears in the original patent but forms no part of this reissuespecification; matter printed in italics indicates the additions made byreissue.

This invention relates to pure fluid devices for measuring the angularrate of rotation of a body about an axis and particularly to improvedfluid readout means for such devices.

The state-of-the-art of pure fluid devices has been considerablyadvanced since the basic fluid amplifiers were built and tested at theHarry Diamond Laboratories in 1959. One example of the extent to whichthe state-of-the-art has advanced can be seen in the October 1964 issueof Control Engineering, wherein an all fluid no-moving parts attitudecontrol system for a missile is described. This system is designed totake the error signals of an attitude sensing device and modulate andamplify these signals to ultimately control the attitude of the missile.Since the control system is designed to be all fluid-operated andwithout moving parts, the output from the attitude sensing device mustbe in the form of fluid signals in order for the sensor to be compatiblewith the rest of the system.

One type of pure fluid attitude sensor that has been used to supply theerror signals for the missile control system is the fluid-operatedrotation sensing device disclosed by Romald E. Bowles in his patentapplication Ser. No. 171,538, 'now US. Pat. No. 3,320,815, filed Feb. 6,1962, and assigned to the assignee in the instant application. TheBowles rotation sensor is commonly referred to in the art as a vortexrate sensor because it operates on the principles of vortex motion.

The operation of a vortex rate sensor can-be easily understood byconsidering a relatively flat cylindrical chamber having a relativelysmall central drain or output passage therein to which fluid underpressure such as air is supplied at or near the circumference of thechamber. The chamber is provided normally with an annular ring orcoupler made of a porous material such that fluid flowing through thecoupler will have only a radial component of velocity. When the ratesensor is rotated in a plane perpendicular to its axis, a tangentialcomponent of velocity is imposed on the fluid as it leaves the couplerwhereby vortex flow is produced in the chamber and helical flow isproduced in the drain. Because of the conservation of angular momentum,the tangential velocity of the flow and consequently the velocity of thefluid in the vortex increases as the fluid reaches the drain, therebyproviding an amplification factor for the sensor. By appropriatelysensing the flow parameters in the drain, particularly the changes inthe helical angle, the angular rate of the sensor can be determined.

H. D. Ogren in his recently issued US. Pat. No. 3,203,237 entitledVortex Rate Sensor, discloses a readout system for a vortex rate sensorcomprising a movable airfoil member connected to a transducing meanswhereby movement of the airfoil member in response to changes in thehelical flow in the drain will produce an electrical output signalindicative of the angular rate of rotation of the sensor. While Ogrensrate sensor has application to more conventional attitude controlsystemsthat utilize electrical error signals, his

2 readout device would not be useful in an all fluid control system suchas contemplated above.

The Bowles rate sensor mentioned above provides the fluid readoutrequired by an all fluid'attitude control or guidance system, butconsiderable difficulty has been encountered with the Bowles rate sensorin producing an output signal that has a high signal-to-noise ratio anda high sensitivity.

The instant invention is concerned with basically two types of fluidreadout means or pickoffs for a vortex' rate sensor. The first type ofpickoff is employed when the device driven by the sensor has a highinput impedance and requires relatively low flow, and the second isemployed when the device driven by the sensor has a low input impedanceand requires relatively large flow.

At this point it would be useful to consider briefly the properties ofvortex sink flow, so that the invention can be more readily understood.

Vortex motion can be divided into two distinct types of motion, theforced vortex and the free vortex. The forced vortex occurs when allparticles of the fluid have the same angular velocity and, therefore,the tangential velocity, V,, is directly proportional to the radius.This is equivalent to solid body or wheel-like rotation and is sometimesreferred to as rotational flow. As the radius increases, the tangentialvelocity increases linearly. In the free vortex where the flow isirrotational, the tangential velocity, V,, varies inversely with theradius. Also, the centrifugal force decreases with increasing radius.Both of these vortex conditions occur naturally in real vortex motionwith certain limitations.

In free inviscid vortex motion conservation of angular momentum isassumed. When the total pressure is cannot exceed the maximum velocitygiven by I mur. 2/P( lum! xmrir) Thereal vortex motion then has bothforced vortex motion near its axis and free vortex motion at somedistance from its axis. Separating those two regions is a transitionregion where the tangential velocity reaches a maximum. This tangentialvelocity distribution is characteristic for all real vortex devices. Themaximum tangential velocity, V,, occurs at a small radius from thecenter which defines a circle called the limit circle. For maximumsensitivity of the rate sensor; therefore it is desirable to position apick-off in the vicinity of the limit circle so that the maximumtangential velocity and consequently the maximum pressure change can besensed.

It is, therefore, an object of the present invention to provide a vortexrate sensor having improved fluid readout means.

Another object of the instant invention is to provide a vortex ratesensor that produces fluid output signals having a high signal-to-noiseratio.

A further object of the instant invention, is to provide a vortex ratesensor that is sensitive throughout a wide range of changes in the flowdirection.

Still another object of the present invention is to provide a vortexrate sensor that produces fluid output sig- 3, nals for fluid deviceswhich have" high input impedances.

Yet another object of this invention is to provide a vortex rate sensorthat produces fluid output signals for fluid devices which have lowinput impedances.

In accordance with one aspect of the present invention, the foregoingand other objects are attained by providing pickoff means in the drainof a vortex rate sensor that comprises a slotted cylinder positionedwith its axis transverse to the drain axis wherein the slots are locatedin the upstream portion of the cylinder and are at a very small radiusfrom the drain axis. The slotted cylinder acts like a direction-findingpitot tube to measure the changes in the angle of the helical flowthrough the drain produced when the rate sensor is rotated in a planeperpendicular to its axis. As the helical angle changes, the staticpressure at the slots changes, and the pickoff produces a fluid outputsignal that is proportional to the angular rate of rotation of thesensor.

In accordance with another aspect of the invention, an airfoil sectionis positioned upstream of and in close proximity with a similarlypositioned slotted cylinder to amplify thechange in helical angle of theflow through the drain as seen by the slotted cylinder.

In accordance with still another aspect of the instant invention anairfoil section is positioned to extend completely across the drain andserves to direct the helical flow to a splitter located downstream ofthe airfoil to produce a high flow output signal that is proportional tothe angular rate of rotation of the sensor.

The specific nature of the invention, as well as other objects, aspects,uses, and advantages thereof, will clearly appear from the followingdescription and from the accompanying drawings, in which:

FIG. 1 is a plan view, partly in section, of a vortex rate sensor;

FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along lines 33 of FIG.2 and shows the positioning of a slotted cylinder pickoff in the draintube,

FIG. 4 is an enlarged cross-sectional view of the pickoff of FIG. 3taken along lines 4-4 of FIG. 3;

FIG. 5 is a prospective view of a slotted cylinder pick off havingcircumferential slots;

FIG. 6 is a cross-sectional view of a portion of the drain tube of avortex rate sensor which shows an airfoil section in combination withthe slotted cylinder pickoff of FIG. 3;

FIG. 7 is an elevation partly in section taken along lines 77 of FIG. 6;

FIG. 8 is a cross-sectional view showing a modified drain tube accordingto the instant invention which shows an airfoil section in combinationwith a splitter and multiple-flow output means;

FIG. 9 is a plan view, partly in section, taken along the lines 99 ofFIG. 8;

FIG. 10 is-a plan view, partly in section, taken along the line 10-10 ofFIG. 8; and

FIG. 11 is a graphical representation of the tangential velocitydistribution for the combined vortex sink flow.

Referring now to the drawing wherein like numerals designate identicalor corresponding parts throughout the several views, and moreparticularly to FIGS. 1 and 2 where there is shown a vortex rate sensorgenerally indicated by the reference numeral 10. Rate sensor 10 isessentially a relatively flat, hollow, cylindrical chamber that includesa circular top wall 11, a circular bottom wall 12 in spaced parallelrelation thereto, and an annular side wall 13 secured in a fluid tightrelation to the top and bottom walls by any suitable means such as thescrews 14. An annular porous ring or coupler 15 is positioned within thechamber of the rate sensor at a smaller radius than annular wall 13 andprovides a manifold 16 between coupler 15 and annular wall 13. Top andbottom walls 11 and 12, respectively, and annular wall 13 may beconstructed of any rigid material such as metal, glass, plastic or thelike that is compatible with and impervious to the working fluid.Coupler 15 is preferably made of a sintered metal but may be made of anysuitable porous material that allows fluid to pass through it with aminimum of restriction.

Fluid under pressure from a source (not shown) enters rate sensor 10 bymeans of one or more input nozzles 17 formed in the annular wall 13, andleaves the rate sensor by means of a centrally located drain tube 18provided in the bottom plate 12 to be discharged to the ambientcondition or to a sump (not shown). While only one drain is shown, itwill be obvious that a second drain may be provided in the top plate 11if desired.

Positioned within drain tube 18 is a fluid readout means 19 whichconsists essentially of a thin-walled cylindrical tube that extendsthrough the wall of the drain tube 18 and into the drain passage 21formed thereby to the central axis AA. Readout means 19, referred toalso as a pickoff, senses changes in the fluid flow leaving the ratesensor 10 and transmits these changes as fluid output signals tosuitable fluid elements (not shown) in the rest of the control system ofwhich the rate sensor forms a part. In the missile guidance systemmentioned above, the fluid output signals from the rate sensor 10 aretransmitted to the inputs of a fluid pulse width modulator such asdisclosed by Warren et al. in their application Ser. No. 3l2,808, nowUS. Pat. No. 3,228,410, filed Sept. 30, 1963, for Fluid Pulse WidthModulation. In another application, the fluid output signals produced bypickoff 19 might be amplified by means of a proportional fluidamplifier.

The details of pickoff 19 can be more readily appreciated with specificreference to FIGS. 3 and 4. Pickoff element 19 is preferably a slotted,hollow cylinder,

closed at one end, which extends into the drain of sensor 10 with itsaxis perpendicular to the drain axis which is also the sensor axis A-A.This pickoff element senses changes in the flow direction in drainpassage 21 in one embodiment by means of a pair of parallel arrangedaxial slots 22 and 23 which extend through the pickoff cylinder wall 24and into a pair of separate output channels 25 and 26, respectively,which are formed by a wall member 27. The operation of the slottedcylinder pickoff 19 can be explained by referring to the two dimensionalflow around a circular cylinder whose axis is perpendicular to the flowsome distance ahead of the cylinder. The pressure distribution aroundsuch a cylinder is shown in FIG. 4 by the distribution of the pressuredifference, p p somewhat as represented by the radial ordinates in FIG.4, and b P p/2(4Vo sin 6) H where H is the total pressure, p is thedensity, V is the fluid velocity, p is the pressure at the angle 0, and0 is the angle measured from the stagnation point on the cylinder. Atthe stagnation point the pressure difference is P Pb p f When anaperture is provided in the surface of the cylinder, such as slots 22and 23," at the critical angle 6,

the pressure at this point is static. The slotted cylinder pickoff 19can be positioned with the slots at any desired 0. When the angle of thehelical flow through the drain passage 21 is changed, as by a change inthe angular rate of rotation of the sensor, the stagnation point on thecylinder shifts and the static pressure at the slots changes therebyproducing a signal that is dependent on the angular rate of rotation ofthe sensor. The change in the pressure measured at a point on thecylinder with respect to a change in the stagnation point is given bytip/d6 4pV,, sin 0 cos 0 V the axial velocity of the fluid stream in thedrain, can be calculated approximately by use of the continuity equationif the flow is considered incompressible and isothermal.

The rotation of the rate sensor in a plane perpendicular to its axiscauses the flow to move at an angle a to the axis of the drain. Forsmall deflections, this angle is approximated by tan a a V,V where V isthe average flow velocity in the drain and V, is the tangential velocityat the slots on the pickoff which is found from the law of conservationof angular momentum. For a unit mass of fluid, 8M,

fwnln, where r is the radius at the pickoff slot, r, is the couplerradius and ru is the angular velocity of the sensor. It can be shownfurther that rotation of the rate sensor changes the stagnation point bythe same angle a, which is equivalent to changing the angular positionof the pickoff slot by an angle a.

By way of specific example, two types of slots for the cylindricalpickoff are shown. First, an axial slot such as 22 or 23, which averagesthe radial velocity distribution, and second, a circumferential slotsuch as 28 or 29, shown in FIG. 5, which averages the pressuredistribution around the pickoff 19. The output of the axial slot typepickoff depends on l/r where r, is the radius of the drain at thepickoff slot. Because of the limit circle at the center of the vortexproduced in the drain, the actual output does not increase as rapidly asmight be expected from a consideration of dp/dw. The output of thecircumferential slot type pickoff depends on sin 26. By averaging thisparameter over the angular length of the slot it can be shown that themaximum output occurs at 45; therefore, the average slot position shouldbe placed at 45 from the stagnation point. In the axial slotted case,for maximum output, the angular position of the slot is alsoapproximately 45. The circumferential slot should be placed at a smallradius, r so as to obtain a relatively large helical angle.

The size of the pickoff slot is determined by the input impedance of thepure fluid device to be driven by the sensor. If the device has a lowinput impedance, the slots must be large to supply flow. If the deviceon the other hand has a high input impedance, the slots should be smallwhich will give a larger output pressure. The sensor works best withhigh input impedance devices, since the maximum sensitivity occurs forsmall slots. Because averaging over the circumferential slot does notreduce the pressure signal as much as averaging over the axial slot,circumferential slots appear to be better for low impedance devices. Thepresent vortex rate sensor employing slotted cylinder pickoffs forproducing pure fluid output signals can be made a pushpull device byproviding one cylinder per drain in a 6 double drain type rate sensor asmentioned above, with each cylinder having a single slot positioned atthe optimum angle 6 from the stagnation point.

Also, while the cylindrical pickoffs 19 are shown to extend only to thecentral drain axis AA. cylinder 19 may extend complete-1y across thedrain opening 21 along the axis BB shown in FIG. 3. This arrangementproduces somewhat less noise and is easier to construct.

To increase the amplitude of the pressure signal produced by acylindrical slotted pickoff, an airfoil section 31 is inserted in drainpassage 21, a short distance upstream of slotted cylinder 19. Airfoilsection 31 is preferably a symmetrical airfoil that possesses a highcoefficient of lift to drag ratio, and is positioned with the chord ofthe airfoil in line with the direction of the drain flow for aparticular initial condition of rotation of the sensor. In mostsituations, the chord of the airfoil section 31 coincides with the drainaxis AA. The angle between the chord of the airfoil section and eitherslot 22 or 23 should equal the optimum angle 0, but it is contemplatedthat this angle can be varied for purposes of biasing the rate sensor.The airfoil section 31 senses a change in the helical angle a of theflow in the drain as a change in angle of attack. When the angle ofattack is not zero, the flow velocity on one side of the airfoil isgreater than the flow velocity on the other side of the airfoil. Whenthese flows of different velocities meet at the trailing edge 33 of theairfoil 31, the angle a between the direction of this flow and the drainaxis AA is considerably greater than the angle of attack at the leadingedge 32. Slotted cylinder 19 which extends into the drain passage 21under and along the trailing edge 33 of airfoil 31 sees the change inthis flow direction as a change of angle of attack resulting in adifferential pressure across slots 22 and 23.

The fluid output signal produced by slotted cylinder 19 in combinationwith the symmetrical airfoil section 31 is in the order of ten timesgreater than the fluid output signals produced by the slotted cylinderalone. The reason for the increased sensitivity of this combination isof course that the angle of deflection oz in the flow at the trailingedge of airfoil section 31 is greater than the helical angle a of theflow in the drain upstream of the airfoil section. In FIG. 7 airfoilsection 31 is shown to extend half way across drain passage 21, but itis advantageous in some instances to have airfoil section 31 extendcompletely across the passage. Cylindrical pickoff 19 likewise canextend completely across the passage for the reasons given above.

Because of turbulence that exists along the trailing edge of an airfoilsection caused by vortices generated along this edge, an alternatearrangement is to position the cylindrical pickoff a small horizontaldistance away from axis AA and the chord of the airfoil. It is alsocontemplated that an airfoil section such as 31 may be positionedupstream and between a pair of slotted cylinder pickoffs that areseparated from one another a short distance on either side of thecentral axis with the cylinders having only a single slot and one outputchannel each as compared to the double channel output pickoff describedabove.

The vortex rate sensor pickoff techniques disclosed in FIGS. 2 through 7are utilized to produce pressure type output signals with relatively lowflow. When a high flow signal is required that is proportinal to theangular rate of rotation of the sensor, the pickoff arrangement shown inFIGS. 8 through 10 is employed.

A symmetrical airfoil section 41 having a high coefficient of lift todrag ratio is installed in the drain 40 of a vortex rate sensortransverse to the drain axis A-A with the chord of the airfoil sectionorientated for a particular drain flow condition but typicallycoinciding with the drain axis AA and extending completely across thedrain opening as more clearly shown in FIG. 9. Airfoil section 41 ispreferably positioned in an expanding portion 42 of the drain 40 foroptimum efficiency. Below the airfoil section 41, or downstream, thedrain becomes four equal output channels 44, 45, 46, and 47 which areformed by a double splitter 43.

When the vortex rate sensor is rotated in a plane perpendicular to itsaxis AA, a vortex is generated in the chamber (not shown), and a helicalflow is generated in the drain 40. The airfoil section 41 sees thehelical angle a as an angle of attack and when this angle is not zero,the velocity on one side of the airfoil is greater than the velocity onthe other side. At the trailing edge where these two streams ofdifferent velocities meet, a deflection of the drain flow occurs in theexpanded region 42 of the drain 40 which produces a differential flowacross splitter 43. As a result of the deflection of the drain flowcaused by airfoil section 41, a differential flow is produced across thesplitter 43.

Assuming a counterclockwise rotation of the rate sensor as indicated bythe direction of w in FIG. 1, helical flow having a counterclockwisedirection will be produced in drain 40, as shown by the arrow V,, inFIG. 9. This flow will result in the higher velocity flow leaving theoutput channels 45 and 46 and the lower velocity flow leaving the drainvia output channels 44 and 47 as shown by the plus and minus signs,respectively, in FIG. 10. The double splitter 43 in dividing the draininto 4 equal output channels provides a dual push-pull output.

The flow output signal produced in the output channels 44 to 47 becomethe input signals for an appropriate pure fluid device (not shown)having a low input impedance. Airfoil section 41 can alternatively beinstalled in drain 40 to extend only as far as the drain axis AA in acantilevered manner such as in the airfoil and slotted cylinderarrangement shown in FIG. 7. This construction will tend to increase theoutput flow but it will also result in somewhat more noise in the outputsignal.

High flow output signals can also be produced by means of a flow dividerdevice in the drain such as shown in FIGS. 8-10, but not including anairfoil section upstream thereof. A pickoff arrangement without anairfoil section will result in less noise being produced in the outputsignals but will probably sacrifice the sensitivity associated with anairfoil section being present in the drain upstream of the divider. Inthis arrangement, the sensitivity can be increased to a certain extentby positioning one of the diametrical edges of the double splitter 43 aslight distance upstream of the other.

In the pickoff arrangements employing slotted cylinders as shown inFIGS. 27, the openings are positioned in the drain to produce an outputsignal in the form of a pressure change that is proportional to theangular rate of rotation of the sensor. From a consideration of apressure and velocity distribution curve such as shown in FIG. 11, whichis taken for actual vortex flow including viscous effects which were notconsidered in arriving at earlier equations, of a portion of the fluidin the region of the drain near r rotates like a solid body and thetangential velocity V, then varies as the product of rw. Outside thiscentral core of solid body rotation is a transition region. Outside thetransition region the fluid flows as in a free vortex, where tangentialvelocity V, varies as K/r. From the curve shown in FIG. 11, it can beseen that the region of the highest tangential velocity, andconsequently the region of highest pressure, is located in thetransition region.

It, therefore, becomes apparent that the optimum position for theopening in the cylindrical pickoff should be located at a radius 1',-which corresponds to the midpoint of the transition region. However,since the transition region and the radius r, are extremely difficult tolocate and because the opening should be sufficiently large enough toproduce a usable output signal, the opening in the cylinder will in mostinstances be large enough to extend across the entire transition region.

In dealing with vortex sink flow as with most any other kind of fluidflow, it is very important that edges and abrupt changes in the shape ofthe walls containing the fluid be avoided to reduce turbulence. For thisrea' son, the entrance to the drain tube 18 in the vortex rate sensor 10is shown to have a smoothly curved edge 20 to reduce turbulent effectswhich, of course, result in the noise in the output signals from therate sensor.

In one embodiment of our invention, the following dimensions areemployed. The inside diameter of coupler 15 is 3.625 inches. The heightof the chamber is .1 inch. Drain passage 18 has an inside diameter of.080 inch. Circumferential slots 28 and 29 have a length of .010 inch, awidth of .008 inch and are located at an average or mean radius r, of.005 inch. These dimensions are merely illustrative and we do not wishto be limited thereto.

It will be apparent that the embodiments shown are only exemplary andthat various modifications can be made in construction and arrangementwithin the scope of the invention as defined in the appended claims.

We claim as our invention:

1. In a pure fluid device for sensing the angular rate of rotation of abody about an axis including a vortex chamber having a circularcross-sectional area, means for introducing pressurized fluid into saidchamber with substantially only a radial component of velocity and acylindrical drain passage located at the center of said chamber with theaxis of said drain passage coinciding with the axis of said chamber andbeing parallel to the axis of said body, whereby upon rotation of saiddevice in a plane perpendicular to the axis of said body vortex flow isgenerated in said chamber and helical flow is generated through saiddrain passage, improved fluid readout means for said device for sensingchanges in said helical flow as a measure of the rate of rotation ofsaid device comprising:

(a) a hollow cylindrical pickoff tube located in said drain passage withthe axis of said pickoff being transverse to said drain axis;

(b) a portion of the wall of said pickoff having aperture means forproviding fluid communication between said drain passage and outputchannel means in said pickoff;

(c) said pickoff being orientated in said drain passage with saidaperture means displaced from the axis of said drain by an angle 6 suchthat the pressure produced at said aperture means is substantiallystatic;

(d) said pickoff producing fluid output signals in response to thechanges in the helical angle of said wherein:

I Re. 28,622

9 drain flow asmeasured by correspond'ingchanges in the static pressureat-said aperture means;

(e) whereby said fluid output signals are proportional to theangularrate of said rotation] [2. The rate sensing device according toclaim 1 .(a) the center of said aperture means is located closelyadjacent ,to said drain axis in the vicinity of the radiusof the limitcircle in the transition region of said helical flow produced in saiddrain,

(b) whereby the maximum tangential velocity and consequently the highestpressure of said drain flow will be sensed by said pickoff] [3. The ratesensing device according to claim 2 wherein:

(a) said aperture means comprises a pair of spaced slots with theirrespective centers being separated from each other in'said pickoff wallby an angle equal to 26,

(b) eachof said slots communicating with a separate output channel insaid pickoff for producing fluid output signals in response to thepressure changes sensed at said slots as the helical angle of said drainHow changes,

(c) whereby said fluid output signals are proportinal to said rate ofrotation of said device] [4. The rate sensing device according to claim3, wherein said slots are parallel to each other and are axi-t allarranged in said pickoff wall.]

5. The rate sensing device according to claim 3, wherein said slots arecircumferentially arranged] [6. The rate sensing device according toclaim 3, wherein the angle 6 equals approximately 45.]

7. I: In the rate sensing device claim 1, the fluid readout meansfurther comprising:] In a pure fluid device for sensing the angular rateof rotation of a body about an axis including a vortex chamber having acircular cross-sectional area, means for introducing pressurized fluidinto said chamber with substantially only a radial component of velocityand a cylindrical drain passage located at the center of said chamberwith the axis of said drain passage coinciding with the axis of saidchamber and being parallel to the axis of said body, whereby uponrotation of said device in a plane perpendicular to the axis of saidbody vortex flow is generated in said chamber and helical flow isgenerated through said drain passage, improved fluid readout means forsaid device for sensing changes in said helical flow as a measure of therate of rotation of said device comprising: 7

(a) a hollow cylindrical pickoff tube located in said drain passage withthe axis of said pickoff being transverse to said drain axis;

(b) a portion of the wall of said pickoff having aperture means forproviding fluid communication between said drain passage and outputchannel means in said pickoff;

(c) said pickoff being orientated in said drain passage with saidaperture means displaced from the axis of said drain by an angle 6 suchthat the pressure produced at said aperture means is substantiallystatic;

(d) said pickofl producing fluid output signals in response to thechanges in the helical angle of said drain flow as measured bycorresponding changes in the static pressure at said aperture means;

(e) whereby said fluid output signals are proportional to the angularrate of said rotation;

(f) [(a)] an airfoil section located in said drain passage transverselyof said drain axis with the trailing edge thereof being upstream of andin close proximity with said pickoff means,

(g) [(b)] said airfoil section being a symmetrical airfoil processing ahigh coefficient of lift to drag ratio, 7 v v (h) [(c)] said airfoilsection cooperating with said pickoff to provide an amplification of thechanges inthe helical angle of said drain flow to be sensed by saidpickoff slots,

(t) [(d)] whereby the pressureof said output signals is greatlyincreased.

8. [In the ratesensing device according to claim 3, the fluid readoutmeans further comprising] In a pure fluid device for sensing the angularrate of rotation of a body about 'an'axis including a vortex chamberhaving a circular cross-sectinal area, means for introducing pressurizedfluid into said chamber with substantially only a radial component ofvelocity and a cylindrical drain passage located at the center of saidchamber with the axis of said drain passage coinciding with the axis ofsaid chamber and being parallel to the axis of said body, whereby uponrotation of said device in a plane perpendicular to the axis of saidbody vortex flow is generated in said chamber and helical flow isgenerated through said drain passage, improved fluid readout means forsaid device for sensing changes in said helical flow as a measure of therate of rotation of said device ccomprising:

(a) a hollow cylindrical pickoff tube located in said drain passage withthe axis of said pickoff being transverse to said drain axis;

(b) a portion of the wall of said pickoff having aperture means forproviding fluid communication between said drain passage and outputchannel means in said pickoff;

(c) said pickoff being orientated in said drain passage with saidaperture means displaced from the axis of said drain by an angle 6 suchthat the pressure produced at said aperture means is substantiallystatic;

(d) said pickoff producing fluid output signals in response to thechanges in the helical angle of said drain flow as measured bycorresponding changes in the static pressure at said aperture means;

(e) whereby said fluid output signals are proportional to the angularrate of said rotation;

(f) the center of said aperture means being located closely adjacent tosaid drain axis in the vicinity of the radius of the limit circle in thetransition region of said helical flow produced in said drain;

(g) whereby the maximum tangential velocity and consequently the highestpressure of said drain flow will be be sensed by said pickofl;

(/1) said aperture means comprising a pair of spaced slots with theirrespective centers being separated from each other in said pickofi" wallby an angle equal (i) each of said slots communicating with a separateoutput channel in said pickoff for producing fluid output signals inresponse to the pressure changes sensed at said slots as the helicalangle of said drain flow changes;

(j) whereby said fluid output signals are proportional to said rate ofrotation of said device;

(k) [(21)] a symmetrical airfoil section possessing a high coefficientof lift to drag ratio located in said drain passage transversely of saiddrain axis with the trailing edge thereof being upstream of and in closeproximity with said pickoff,

(I) [(b)] said airfoil section being positioned between said pickoffslots such that the angle between the chord of the airfoil and one ofsaid slots is equal to 6,

(m) [(c)] said airfoil section cooperating with said pickoff to providean amplification of the changes in the helical angle of said drain flowto be sensed by said pickoff,

(n) [(d)] whereby the sensitivity of said readout means is greatlyincreased.

9. In a vortex angular rate sensor having a vortex chamber supplied withfluid under pressure, an input manifold, a porous coupler ring, and acylindrical drain passage located at the axis of said chamber andwherein the fluid enters said chamber from said manifold through saidring having substantially only a radial component of velocity, wherebyupon rotation of said rate sensor in a plane perpendicular to said axisvortex flow is generated in said chamber and helical flow is generatedthrough said drain, improved readout means for producing fluid outputsignals indicative of the rate of rotation of said device comprising:

(a) double splitter means extending across said drain passage anddividing said passage into four equal output channels,

(b) the upstream edges of said splitted means being transverse to theaxis of said drain passage,

(c) said splitter means producing a differential flow in said outputchannels in response to a change in said helical flow,

(d) whereby said differential flow results in a high flow output signalin said output channels that is proportional to the rate of saidrotation,

(e) a symmetrical airfoil section possessing a high lift to drag ratiopositioned in an expanded portion of said drain passage upstream of saidsplitter means,

(f) said airfoil section being transverse to the axis of said passage,

(g) said airfoil section cooperating with said splitter means to deflectsaid helical drain flow to produce a differential flow across saidsplitter means,

(h) whereby said differential flow generates high flow output signals insaid output channels proportional to the rate of said rotation.

10. The rate sensor according to claim 9, wherein the edge of oneportion of said splitter means that extends diametrically across saiddrain passage is located a slight distance upstream of the other edgeportion of said splitter means whereby the sensitivity of said readoutmeans is improved.

8. (In the rate sensing device according to claim 3, the fluid readout means further comprising:) In a pure fluid device for sensing the angular rate of rotation of a body about an axis including a vortex chamber having a circular cross-sectinal area, means for introducing pressurized fluid into said chamber with substantially only a radial component of velocity and a cylindrical drain passage located at the center of said chamber with the axis of said drain passage coinciding with the axis of said chamber and being parallel to the axis of said body, whereby upon rotation of said device in a plane perpendicular to the axis of said body vortex flow is generated in said chamber and helical flow is generated through said drain passage, improved fluid readout means for said device for sensing changes in said helical flow as a measure of the rate of rotation of said device ccomprising: (a) a hollow cylindrical pickoff tube located in said drain passage with the axis of said pickoff being transverse to said drain axis; (b) a portion of the wall of said pickoff having aperture means for providing fluid communication between said drain passage and output channel means in said pickoff; (c) said pickoff being orientated in said drain passage with said aperture means displaced from the axis of saiD drain by an angle theta such that the pressure produced at said aperture means is substantially static; (d) said pickoff producing fluid output signals in response to the changes in the helical angle of said drain flow as measured by corresponding changes in the static pressure at said aperture means; (e) whereby said fluid output signals are proportional to the angular rate of said rotation; (f) the center of said aperture means being located closely adjacent to said drain axis in the vicinity of the radius of the limit circle in the transition region of said helical flow produced in said drain; (g) whereby the maximum tangential velocity and consequently the highest pressure of said drain flow will be be sensed by said pickoff; (h) said aperture means comprising a pair of spaced slots with their respective centers being separated from each other in said pickoff wall by an angle equal to 2 theta ; (i) each of said slots communicating with a separate output channel in said pickoff for producing fluid output signals in response to the pressure changes sensed at said slots as the helical angle of said drain flow changes; (j) whereby said fluid output signals are proportional to said rate of rotation of said device; (k) ((a)) a symmetrical airfoil section possessing a high coefficient of lift to drag ratio located in said drain passage transversely of said drain axis with the trailing edge thereof being upstream of and in close proximity with said pickoff, (l) ((b)) said airfoil section being positioned between said pickoff slots such that the angle between the chord of the airfoil and one of said slots is equal to theta , (m) ((c)) said airfoil section cooperating with said pickoff to provide an amplification of the changes in the helical angle of said drain flow to be sensed by said pickoff, (n) ((d)) whereby the sensitivity of said readout means is greatly increased.
 9. In a vortex angular rate sensor having a vortex chamber supplied with fluid under pressure, an input manifold, a porous coupler ring, and a cylindrical drain passage located at the axis of said chamber and wherein the fluid enters said chamber from said manifold through said ring having substantially only a radial component of velocity, whereby upon rotation of said rate sensor in a plane perpendicular to said axis vortex flow is generated in said chamber and helical flow is generated through said drain, improved readout means for producing fluid output signals indicative of the rate of rotation of said device comprising: (a) double splitter means extending across said drain passage and dividing said passage into four equal output channels, (b) the upstream edges of said splitted means being transverse to the axis of said drain passage, (c) said splitter means producing a differential flow in said output channels in response to a change in said helical flow, (d) whereby said differential flow results in a high flow output signal in said output channels that is proportional to the rate of said rotation, (e) a symmetrical airfoil section possessing a high lift to drag ratio positioned in an expanded portion of said drain passage upstream of said splitter means, (f) said airfoil section being transverse to the axis of said passage, (g) said airfoil section cooperating with said splitter means to deflect said helical drain flow to produce a differential flow across said splitter means, (h) whereby said differential flow generates high flow output signals in said output channels proportional to the rate of said rotation.
 10. The rate sensor according to claim 9, wherein the edge of one portion of said splitter means that extends diametrically across said drain passage is located a slight distance upstream of the other edge portion of said splitter means whereby the sensitivity of said readOut means is improved. 